Built within Louisville International, Worldport accounts for about 80 percent to 85 percent of flights in and out of the airport. UPS' facility accounts for nearly all flights there during the busier night shift.

Large swaths of the metal floors have wheels and ball bearings built into them, allowing workers to haul around big containers -- called "unit load devices," or ULDs -- filled with shipping boxes inside.

When you walk around inside, you hear a loud and constant drone of machines, mixed with the whir of fans. A lot of the facility is dimly lit. Workers are all over the floor, moving around, sorting, loading and unloading packages.

Shipping containers hold all kinds of weirdly shaped items, including car mufflers with shipping labels slapped on them. These irregulars are placed on sled-shaped holders, like the one seen here, to send the pieces through the conveyor belts.

Small packages and documents are pushed from rows and rows of conveyor belts onto ramps, where they're placed inside "forever bags," which are named that because they're supposed to last, you know, a long time.